The Startup Disk icon is a shortcut that appears by default on the Mac desktop. You can organize your desktop by hiding the Startup Disk icon from your desktop, using your General Preferences in Finder.

Launch Finder by clicking on the "Finder" icon on your desktop.

Click on Finder's main heading titled "Finder" next to the File heading.

Click on "Preferences" in the drop-down box under the Finder heading and select the "General" section.

Deselect the "Hard disks" option under the "Show these items on the Desktop" in Finder's General Preferences.